Display apparatuses such as mobile phones, tablet computers, and other portable devices have been widely used in people's daily life. In recent years, a significant amount of research efforts has been made to increase the operational time of the display apparatus, e.g., by prolonging the viability of the battery. In a conventional portable display apparatus such as a mobile phone, the backlight is automatically turned off when no user operation is detected after a period of time, even if the user is still viewing a display on the portable display apparatus. This design is not user-friendly.